A trunking communication system refers to a dedicated mobile communication system in which multiple users share and dynamically use a group of radio channels, and the trunking communication system is mainly used for the command and dispatch communication. The trunking communication systems include analogue trunking systems and digital trunking communication systems. The Digital Mobile Radio (DMR) trunking communication system based on the DMR trunking protocol is a digital trunking communication system. The current trunking communication system has the shortcomings of low channel utilization ratio, low system capacity, poor anti-interference performance and so on.
The frequency hopping communication technology, in which the frequency hops in different frequency points according to certain rules, has good anti-interference and anti-capture capabilities, and is mainly used for military communication. Civilian communication such as Bluetooth technology also uses frequency hopping communication. In view of the shortcomings of the current trunking communication system, introducing frequency hopping technology in the DMR trunking communication system based on the DMR protocol can improve the channel utilization ratio, greatly enhance the system capacity, and has good anti-interference capability.
One of the main difficulties in frequency hopping communication is design of the frequency hopping synchronization algorithm. Frequency hopping synchronization must meet the requirements that both sides of the communication have the same hopping frequency table, the same frequency hopping sequence, the same start and end time of hopping frequency. It can be considered that the performance of frequency hopping synchronization determines the performance of frequency hopping communication system, and the design of hopping synchronization is particularly important. The current frequency hopping synchronization methods include independent channel method, self-synchronization method and synchronization prefix method. Independent channel method is to utilize a separate physical channel for announcing information needed for frequency hopping synchronization; self-synchronization method is to extract a synchronization signal from the received information; and synchronization prefix method is to send synchronization messages (Time Of Date information, referred to as TOD information) for frequency hopping synchronization with variable frequency points selected from a matrix of frequency points prior to sending information. The disadvantage of the independent channel method is that it requires a separate physical channel to send synchronization information and confidentiality is poor, while the advantage is that the amount of the transmitted synchronization information is large and the synchronization establishing time is short; the self-synchronization method can carry less synchronization information and its synchronization establishing time is too long; synchronization prefix method is a compromised scheme with the drawback that the implementation is technically difficult and thus the cost of the product is relatively high.
Due to the fact that the frequency hopping synchronization is the most basic synchronization in the frequency hopping communication and failure in synchronization means communication failure, it is needed to find a frequency hopping synchronization method based on the variety of current synchronization methods, which combines the characteristics of the DMR trunking system, has low technical difficulty in implementation and has good performance, thus enhancing the overall technological content of products and product quality.
At present, the frequency hopping communication technology is not utilized in the trunking communication system. The frequency hopping methods of the digital frequency hopping system now mainly include self-synchronization method, synchronization prefix method and independent channel method. In the self-synchronization method, synchronization information is hide in information sequence transmitted by a transmitter and is extracted by a receiver. The specific implementations of the self-synchronization method now include the FFT (Fast Fourier Transform) method and the window sliding method. The FFT method performs FFT operation in the medium frequency, and implements frequency hopping synchronization by frequency points hopping. The window sliding method performs operation to implement frequency hopping synchronization through window sliding; synchronization prefix method sends synchronization information (TOD information) for the frequency hopping synchronization by using the frequency matrix before sending information, and the receiver must capture the synchronization information to perform synchronization within a limited time period; independent channel method uses a separate physical channel to announce information required for frequency hopping synchronize.
In the self-synchronization method, the time for establishing synchronization is long due to the large operation amount and the long operation time, and the available information amount that may be extracted is small; in the synchronization prefix method, transmission power is lost because synchronization information has to be sent for each communication, and the receiver has to extract information quickly, incurring high technical difficulty in implementation and poor concealment; the independent channel method requires a dedicated physical channel, and confidentiality is not strong. Because there is no trunking communication system using frequency hopping technology, using any one of the above various synchronization methods alone does not combine the characteristics of the trunking communication system well.